A conventional ink jet head for discharging ink onto a recording medium to print an image or the like has a channel unit and a piezoelectric actuator unit. The channels which include nozzles and pressure chambers are formed in the channel unit. The actuator unit applies pressure on the ink in the pressure chambers. For example, Japanese Unexamined Patent Publication No. 8-230182 discloses an ink jet head including a head board and a piezoelectric actuator unit. The head board has pressure chambers formed in it. The actuator unit includes a vibration plate, a metallic conductive layer and piezoelectric elements. The vibration plate lies on the head board and covers the pressure chambers. The conductive layer is formed on the outer side of the vibration plate. Each of the piezoelectric elements is formed on the outer side of the conductive layer over one of the pressure chambers, with a terminal interposed between the piezoelectric element and the conductive layer. Another terminal is formed on the outer side of each of the piezoelectric elements. The terminals on the outer sides of the piezoelectric elements are connected to a flexible cable or another wiring means via an anisotropic conductive sheet. When voltage is applied to some of these terminals through the wiring means, electric fields act on the associated piezoelectric elements to deform them. The deformation of these piezoelectric elements results in the vibration plate being deformed to apply pressure on the ink in the associated pressure chambers.
Japanese Patent No. 3267937 (Corresponding to U.S. Pat. No. 6,471,342 B1) discloses an ink jet head including a head body (a channel unit) and a vibration plate as a common electrode. The head body has pressure chambers formed in it. The upper surface of the vibration plate is patterned with piezoelectric elements and individual electrodes. Each of the piezoelectric elements and each of the individual electrodes are positioned over one of the pressure chambers. Other piezoelectric elements are formed over the portions of the head body between adjacent pressure chambers. Wires (conductors) are formed on these piezoelectric elements. Drive voltage can be supplied through the wires to the individual electrodes. Electric contacts are concentrated at an end of the head body. This facilitates the wiring for the contacts and enables close arrangement of the pressure chambers.
In the ink jet head disclosed in Japanese Unexamined Patent Publication No. 8-230182, wires extend over the piezoelectric elements. Terminals of the wires are connected to the terminals on the outer sides of the piezoelectric elements. Accordingly, if external force is exerted on the wires, they are liable to come off the piezoelectric elements. This reduces the reliability of the electric connection between the terminal on the outer side of each of the piezoelectric elements and the associated wire. In order for this ink jet head to be small in size with its high-speed and high-quality printing performance maintained, its nozzles may be arranged densely. In this case, the pressure chambers, the piezoelectric elements and the terminals are arranged densely because each of the nozzles is associated with one of the pressure chambers, one of the piezoelectric elements and two of the terminals. The wires connected to the densely arranged terminals need to be spaced at narrow intervals. This raises the wire production cost.
In the ink jet head disclosed in Japanese Patent No. 3267937 (Corresponding to U.S. Pat. No. 6,471,342 B1) wires extend on the piezoelectric elements over the partition walls between adjacent pressure chambers. This results in the generation of undesired capacitance (parasitic capacitance) between the vibration plate as the common electrode and each of the wires. This also results in deformations of the piezoelectric layers over the partition walls. The deformations result in deformations of the piezoelectric layers over the pressure chambers, causing so-called crosstalk.